In about a dozen repetitions of the experiment, the team of scientists produced 17 atoms of mendelevium, which were identified by the ion-exchange adsorption-elution method (mendelevium behaved like its rare-earth homologue thulium) and by the electron-capture decay of its daughter isotope fermium-256. Fifteen other isotopes of mendelevium, all radioactive, have been discovered. The stablest is mendelevium-258 (51.5-day half-life). Studied by means of radioactive tracer techniques, mendelevium exhibits a predominant +3 oxidation state, as would be expected by its position in the actinoid series; a slightly stable +2 oxidation state is also known.

any of a series of 15 consecutive chemical elements in the periodic table from actinium to lawrencium (atomic numbers 89–103). As a group, they are significant largely because of their radioactivity. Although several members of the group, including uranium (the most familiar), occur...

in chemistry, the organized array of all the chemical elements in order of increasing atomic number—i.e., the total number of protons in the atomic nucleus. When the chemical elements are thus arranged, there is a recurring pattern called the “periodic law” in their properties,...

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synthetic radioactive element created by helium-ion bombardment of einsteinium-253 in a cyclotron. There are 4 known isotopes. It was the first element to be synthesized and discovered one atom at a time-in 1955 by Albert Giorso, B.G. Harvey, G.R. Choppin, A.G. Thompson, and G.T. Seaborg.